Densifying fine powders



Sept. 17, 1957 c. R. CUTHBERTSON ETAL DENSIFYING FINE pownms Filed July 16. 1952 INVENTOR. 1' CMI'IBSWCM nited St ws.

DENSIFYING FINE PGWDERS Charles Russell Cuthhertson and Orlando Leonard Bertorelh, Berger, Tex, assignors to J. M. Huber Corporatron, Berger, Tex., a corporation of New Jersey Application duly 16, 1952, Serial No. 299,226 5 Claims. (Cl. 23-613) This invention relates to a new method for the removal of air from fine powders and more particularly for increasing the bulk density of fine powders before packaging them. By fine powders we'mean amassed particles of the order of 5 microns or less in greatest dimension.

Many products, especially fine powders used as fillers or pigments in rubber compounds, paints, inks, cosmetics, coanng compositions, or the like, are composed of extremely fine particles whichtend to bridgeand hold occluded air so that the powder normally is'quite fiufiy and may have a bulk density of only a few pounds per cubic foot. Some of these powders increase somewhat in apparent density on long standing, while others bridge air between the particles so tenaciouslythat densification on standing is very slow. Such products are quite expensive to package because of the large amount of package materialrequired, and they are expensive to transport because of the small Weight of material that can be placed in a railway car or motor truck.

- It is the main purpose of the present invention to provide an efiicient method for the removal of air from fine powders, which very substantially increases their bulk density and achieves important savings in the costs of packaging and transporting such powders. Another purpose is to provide such a method by which fiuffy fine powders can'be increased greatly in bulk density without being converted into objectionably coherent aggregates or factory for more than'a limited kind of fine powders.

Fine powders which are'naturally agglomerative, such as carbon black, can be successfully'densified by agitating or tumbling them in a slowly rotating drum; but substances which are not agglomerative, such as fine powders of kaolin, do not respond to this treatment.

. Fine powders of various kinds have been increased in bulk density by placing them in paper or cloth bags and then pressing the bags and their contents to expel air;

but'in such methods the material is packaged in a fiufr'y condition, and no saving is realized in the cost of packagg V. I p

, According to another known method, some densifica- .tion of fine powders can be obtained by placing the powders in a closed container, evacuating-air from the container, and then suddenly introducing air at such a rate thatthecontainer-v isfilledin aboutone second. The

'removal'of the air does not cause a noticeable decrease in the bulk of the powder and sometimes actually causes an increase, but the air rushing in through the pigment carries somepowder in the direction of air fiowand achieves a limited degree of densification.

Fine powders have also been pressed in'solidmctal" containers by means of a moving piston, but this method has not been successful because the air is trapped and compressed along with the pigment; When the pressure is released cracks form throughout: the compressed mass due to the pressure of the Patented Sept. 17, 1 7

trapped air, and much of the densification is lost.

According to the present invention, it has been found that fiufify fine powders can be successfully densified by subjecting them to the action of suction filters similar to those commonly employed for the extraction of liquids from finely divided filterable solids by vacuum. When a finely apertured filtering medium, such as a filter cloth of the type used in ordinary suction filters, is contacted with a fiuify fine powder at one side of the medium while being held under vacuum over its other side,'air is drawn through the powder and carries much of the powder along with it toward the filter medium. Inthis manner a layer of the pow er can be rapidly accumulated on the filtering medium, and the application of suction-to the powder forming. this layer removes much of the air occluded or bridging particles in it and thus compacts it so that a fine powder having a bulk' density much greater than that of the original powder can be obtained from the filtering medium. The bulk density of this suction-compacted powder generally is atleast nearly twice that of the original powder.

Moreover, although the suction-compacted layer still consists of discrete fine powder particle's, it is found, to be sufficiently coherent while suction is, applied to it that it will adhere to. and'canrbe moved, with the filtering medium in any position of the filtering medium. TThis characteristic is utilized according to the present invention for the provision of a continuous method of fine powder densification, or for achieving a further increase of the densityof the powder, and preferably for both purposes. It has been 'found that the bulk density of the suctioncompacted layer can be very substantially increased by mechanically compressing the free side of the layer while continuing to, applysuction to the other side. -In this way, more of the bridging of the pigment particles is destroyed, and the air displaced by the mechanical cornpressionis immediately carriedjaway by the suction so as to yielda compacted or densified powder layer of decreased thickness which has a considerably higher bulk density than the suction-compacted layer.

' The accompanying drawings schematically illustrate practical embodiments of this invention. In the drawings, V n

Fig. 1 shows diagrammatically a manner of accumulating and compacting a mass of fine powders on a filtering medium by the application of suction through the filtering medium;

Fig. 2 shows a layer obtained according to Fig. 1. as it is, carried by the filter, and. after having been trimmed in preparation for further. densification by mechanical compression} 1 p I Fig. 3 shows :a layer of densified powder as obtained from the compression step;

Fig. 4 is a diagrammatic plan Fig. 5; and V H Y 1 Fig. 5 is a diagramma ticvertical cross-section showing an ratus for,tl le contin1'io1 s 'densificau'on of; line powders according to this invention. V

Fig. 6 is a diagrammatic plan viewof the apparatus of Fig.5.

Fundamentals of the method of this invention will be evident from Figs. 1 to 3 -of the drawings, ,A vessel 1 of the apparatus" of holds a very light and flufiy mass of fine powder indicated mass of loose powder z by placing it face downward volume.

- J on the surf ce of the pQ de.

the mass by gravity as the suction through the filter cloth accumulates and compacts powder over the face 1' nd all wing it to sink into.

oi he cloth- .Aiter a iew s qnd u u lly 15 seconds or less, a condition of equilibrium is reached, at which time tl 1 e filter,.ceases to accumulate more powder but holds over its face a clinging mass L of suction-compacted particles. 7.

Wh le continuing the'vacuum, the filter is raised and, if desired, the looser or fringe portions of the layer L aretrimmed or wiped 011 so as to fall into vessel 1, leaving .a trimmed suction-compacted layer L1 clinging :to the surface of the filter cloth. Then the filter is moved to place .thislayer over a flat plate 9, as seen in Fig. 2, and the layer L1 and plate 9 are pressed together to effectuate a .furtherdensification of the powder held on the filter. This yields a further compacted layer as shown diagrammatically at L2 in Fig. 3. The powder .does'not flow away from the filter cloth during this compression step because the vacuum continues to draw .removed'quickly either by the momentary application of a slight superatmospheric air pressure inside the filter leaf or by scraping or cutting off the adherent powder.

7 In thejlatter practice the vacuum may be either released or continued during the removal'of the powder.

The method as described in reference to Figs. 1 to 3 "can be used advantageously for the densification of fine powders of many different substances. For example, it has been used, in the manner and with the results further indicated below, for the treatment of fine powders of *calcium carbonate, of magnesium carbonate, of metasilicic acid, ofcalcium silicate, of kaolin, and of carbon black. All of these powdered substances were composed of particles smaller than' S microns in their largest dimensions. j 7 e v In'eachpffthe uses'me'ntioned, a filter leaf similar to that shown in Figs. 1 to 3 and six (.6) inches in diameter-was employed under an internal pressure of 4 to 8 cms. of mercury. In the first step the leaf was lowered 'onto the surface of the'flufiy fine powder and left to accumulate powder bysuction for '15 seconds. Then the leaf with adherent powder was raised, and the suction-compacted powder layer was trimmed even with the edge of the filter and to a thickness of inch at the face, giving a densified layer of 14.2 cubic inches in V V This layer was removed and weighed to determine its density. Then a second similar. layer was pre- "pared, but before removingthis layer from the filter it .was compressed with a flat plate to a pressure of 5 pounds per square inch and its final thickness was meas ured. Then the compressed layer was removedfrom the filter and weighed to determined its density. V

The densifications thus. achieved appear in the followingptable:

Anembodiment of the invention useful for the large- 4 scale continuous densification of fine powders is illustrated in Figs. 4 and 5 of the drawings.

As there shown, the apparatus makes use of a slowly rotating hollow drum 10 mounted on a hollow shaft 11. The shaft is formed with suction holes 12 which commnnicate with the interior of the drum so that a reduced air pressure can be maintained in the drum by means of a vacuum pump, not shown, connected with the axial bore of the shaft. The shell of the drum is penetrated by a large number of small holes or perforations I13, and its outer surface is covered with a closely fitting mesh screen 14 which in turn is covered by a fine filter cloth 15.

Each end of the drum shell is bordered by a flange 16 which projects slightly beyond the surface of the filter medium held on the shell. A fixed hopper 19 surroundsabout one fourth of the face of the drum and has sides 19a which extend inside the respective end flanges 16 in close relation to these flanges and to the filter cloth 15. Fine powder in a fiuify condition isintroduced into this hopper through a duct 17 whichcontains a rotary star valve 18 for continuous feeding of the powder at any desired rate. The star valve 18 is generally rotated at a speed such that the hopper is kept half or two-thirds filled with the fine fluify pigment.

The rotating drum carries the filter cloth 15 con- .tinuously into and through hopper 19 and into immers ion contact with the mass of flufiy powder held in the hopper. At the same time, vacuum is applied through the shaft 11, the perforations 13 and the filter cloth so as to suck powder to the cloth and withdraw air from the accumulated powder, in the manner already able means (not shown) for any desired adjustment of the space between the roller surface and the surface of e the filter cloth. For example, roller 20 is spaced A to /2 inch from the filter cloth and is'located above hopper opening 19b. This roller serves to force the lightly adherent top layer of the accumulated pigment back into hopper 19 and thus'regulates the amount of suction-cornpacted powder on the filter. From roller 20 the rotating drum carries the layer of densified pigmentbeneath roller 21, and then beneath roller 22. These rollers are adjusted closer to the filter clot-h than roller 20, so as to provide increasing pressures on the densified pigment and 1 thus increase its density beyond that which can be secured by the action of vacuum alone.

Beyond roller 22, a doctoring device or *knife 23 is fixed in the path of the compressed powder layer. This device acts continuously to remove densified material from the rotating drumand deflect the discharged material to .filter cloth but preferably is separated from it by a very small distance so that a very thin layer of pigment will always remain on the cloth; In this way blinding of the filter cloth is prevented.

'While the continuous rotaryapparatusv shown in Figs. 4 and 5 makes use of a drum which is evacuated throughout its interioijother forms of rotary vacuum filter devices may-be employed for the practice of this invention.

For example, it is possible to employ Sectional drum filters like those commonly used in separating solids from liquids, equipped with valve meehanismsjfor applying 'vacuum to any desired sections of the filters. In the use of such filters, air under pressure can be applied automatically to sections holding the densified powder, so as to discharge all the powder from the filter cloth in each cycle of operation of the drum.

The practice and results of this invention are further illustrated by the following particulars of an operation employing apparatus similar to that shown in Fig. 5: The drum used had a diameter of 12 inches and a face 6 inches wide. The drum was operated under a vacuum of- 22 inches of mercury and at a speed of 10 R. P. M. The first roller was set at a clearance of inch from the surface of the drum, while rollers 21 and 22 were set at clearances of and 7 inch, respectively. A flufiEy fine powder of sodium aluminum silicate, composed of particles smaller than 1 micron in their largest dimension and weighing 7.1 pounds per cubic foot, was fed into the hopper of the machine. The operation proceeded continuously as described above, and a densified powder product was removed from the machine at the rate of 7 pounds per minute. This product had a 'bulk density of 25 pounds per cubic foot. When the same operation was performed with the compression rollers 21 and 22 set at inactive positions, a vacuum-compacted powder having a bulk density of 17 pounds per cubic foot was obtained at the rate of 7 pounds per minute.

It will be apparent that this invention may be practised in various ways and is not limited to particulars of the embodiments hereinabove described except as required by a fair construction of the appended claims.

We claim:

1. The method of densifying flulfy fine powder which comprises continuously moving a surface of an endless filtering medium fine enough to separate the powder from air into and through a flufify mass of said powder while applying suction through said surface to powder in such mass, thereby continuously attracting particles of the powder from said mass to said surface, forming a layer of the attracted powder particles on said surface and withdrawing air from and thus compacting powder in said layer; by continuing the application of suction through said surface in a part of its path extending away from said mass, holding to said surface a layer of densified powder so formed and carrying such layer away from said mass on said surface; and discharging densified fine powder from said surface in a part of its path away from said mass.

2. The method of densifying flufiy fine powder which comprises continuously moving a surface of an endless filtering medium fine enough to separate the powder from air into and through a fluify mass of said powder while applying suction through said surface to powder in such mass, thereby continuously attracting particles of the powder from said mass to said surface, forming a layer of the attracted powder particles on said surface and withdrawing air from and thus compacting powder in said layer; by continuing the application of suction through said surface in a part of its path extending away from said mass, holding to said surface a layer of densified powder so formed and carrying such layer away from said mass on said surface; mechanically compressing a powder layer so held and carried to compact further the powder therein; and then discharging densified fine powder from said medium in a part of its path away from said mass.

3. The method of densifying fluffy fine powder which comprises continuously moving a surface of an endless filtering medium fine enough to separate the powder from air into and through a flufiy mass of said powder while applying suction through said surface to powder in such mass, thereby continuously attracting particles of the powder from said mass to said surface, forming a layer of the attracted powder particles on said surface and withdrawing air from and thus compacting powder in said layer; by continuing the application of suction through said surface in a part of its path extending away from said mass, holding to said surface a layer of densified powder so formed and carrying such layer away from said mass on said surface while continuing so to hold and carry said layer on said medium continuously compressing said layer over its free surface at successive zones in its path of movement to compact further the powder in such layer; and then discharging densified fine powder from said medium in a part of its path beyond said zones.

4. The method of densifying fluify fine powder which comprises immersing in a fiufiy mass of said powder a surface of a filtering medium fine enough to separate the powder from air by applying suction through said surface to the powder attracting loose particles of the powder from said mass to said surface, withdrawing air from among the attracted powder particles, and thus forming on said surface a substantial coherent layer of powder containing substantially less air than the powder in said mass; then, while holding such layer to said surface by continuing the application of such suction, separating said surface with such layer thereon from powder remaining in said mass; and thereafter removing from said surface fine powder of said layer having a bulk density substantially exceeding that of said fiuify fine powder.

5. The method of densifying fiufiy fine powder which comprises immersing in a fluffy mass of said powder a surface of a filtering medium fine enough to separate the powder from air by applying suction through said surface to the powder attracting loose particles of the powder from said mass to said surface, withdrawing air from among the attracted powder particles, and thus forming on said surface a substantial coherent layer of powder containing substantially less air than the powder in said mass; then, while holding such layer to said surface by continuing the application of such suction, separating said surface with such layer thereon from powder remaining in said mass and mechanically compressing such layer so as to compact further the powder therein; and thereafter removing from said surface fine powder of said layer having a bulk density substantially exceeding that of said flutfy fine powder.

References Cited in the file of this patent UNITED STATES PATENTS 670,963 Logeman Apr. 2, 1901 695,585 Stanley Mar. 18, 1902 761,878 Cooley June 7, 1904 773,876 Lorillard Nov. 1, 1904 1,460,519 Wadsworth July 3, 1923 2,308,031 Schmitz Ian. 12, 1943 2,365,658 Schumacher Dec. 19, 1944 2,554,968 Thompson May 29, 1951 2,607,435 Dohse Aug. 19, 1952 2,633,074 Davis Mar. 31, 1953 2,700,188 Buresh et a1 Jan. 25, 1955 2,715,755 Jones Aug. 23, 1955 FOREIGN PATENTS 171,206 Great Britain Nov. 17, 1921 

1. THE METHOD OF DENSIFYING FLUFFY FINE POWER WHICH COMPRISES CONTINOUSLY MOVING A SUFACE OF AN ENDLESS FILTERING MEDIUM FINE ENOUGH TO SEPARATE THE POWDER FROM AIR INTO AND THROUGH FLUFFY MASS OF SAID POWDER WHILE APPLYING SUCTION THROUGH SAID SURFACE TO POWDER IN SUCH MASS, THEREBY CONTINUOUSLY ATTRACTING PARTICLES OF THE POWER FROM SAID MASS TO SAID SURFACE, FORMING A LAYER OF THE ATTRACTED POWER PARTICLES ON SAID SURFACE AND WITHDRAWING AIR FROM AND THUS COMPACTING POWER IN SAID LAYER; BY CONTINUING THE APPLICATION OF SUCTION THROUGH SAID SURFACE IN A PART OF ITS EXTENDING AWAY FROM SAID MASS, HOLDING TO SAIS SURFACE A LAYER OF DENSIFIED POWDER SO FORMED AND CARRING SUCH LAYER AWAY FROM SAID MASS ON THE SAID SURFACE; AND DISCHARGING DINSIFIED FINE POWDER FROM SAID SURFACE IN A PART OF ITS PATH AWAY FROM SAID MASS. 